Interoperability between the communication systems of local, state and federal agencies became of paramount importance as a result of the terrorist attacks to the United States on Sep. 11, 2001. In response to these events, the U.S. Department of Homeland Security (DHS) was created to facilitate a national effort to prevent and respond to such acts of terrorism. A major component of the DHS' domestic preparedness initiatives is the ability of First Responders to an emergency situation (including those from local, state and federal agencies) to communicate during the crisis.
A number of interoperability systems have been developed to interconnect users of various communications systems (e.g. trunked radio systems users, conventional radio systems users, public switched telephone network (PSTN) users, cellular telephone users, etc.) to allow them to converse with each other on a day to day basis or during times of crisis. Interoperability is in general based upon known similarities between the systems being interconnected. One obvious similarity is that essentially all of the communication systems for local, state and federal agencies provide for a plain media interface (e.g., base-band analog audio, base-band analog video, plain data, etc.) and typically have access to packet-switched communication systems (or networks). A packet-switched network is defined herein as a network that serves as the medium through which messages may be transmitted between two endpoints or nodes (e.g., between a source and a destination), wherein the message is broken down into a set of units commonly referred to as “packets,” and the packets are transferred across the network.
A commonly used packet-switched network is an Internet Protocol (IP) based network, wherein the message is packetized and routed over the network using the Internet Protocol. The Internet Protocol is an open standard network layer (Layer 3 of the Open Standard Interconnection (OSI) model) routing protocol defined in the Internet Engineering Task Force (IETF) Request for Comment (RFC) 791 and any subsequent corresponding RFC updates as recognized in the art. Since IP-based networks are the types of networks most prevalently used by local, state and federal agencies, existing interoperability solutions are, accordingly, typically IP-based. Such IP-based solutions are desirable mainly because they do not require a costly and, quite frankly, unrealistic replacement of equipment that would be necessary to conform the existing communication systems of all of the various agencies to the same type of radio system, equipment and standards.
Moreover, existing solutions are typically either based upon a client-server networking approach or a peer-to-peer solution for interoperability. When using the client-server approach, a client system that wants to be interconnected with another client system must first communicate with a third-party application (i.e., a server) to facilitate the interoperability and resultant communication with the other client system. Whereas with a peer-to-peer solution, once a logical path is established through a network between, for example, two packet-switched apparatus (i.e., a connection is established), communication frames may be transmitted over the connection without the need for a third-party application (e.g., a server). In other words, once a connection is established between two packet-switched apparatus, communication frames may be transmitted directly from one apparatus to the other over the established connection without any server intervention.
Although systems for interoperability have been developed, there still exists a need for features that enhance communications between two or more distinct communication systems connected using these interoperability systems. For example, talk permit tones, emergency announcements and vocalic radio patch establishment features are three such features that may be extremely useful and desirable in today's interoperability systems.